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Webster 1828 Edition

Noun.

fers'ness.

Ferocity; savageness.

The defect of heat which gives fierceness to our natures.

Eagerness for blood; fury; as the fierceness of a lion or bear.

Quickness to attack; keenness in anger and resentment.

The Greeks are strong, and skilful to their strength,

Fierce to their skill, and to their fierceness valiant.

Violence; outrageous passion.

His pride and brutal fierceness I abhor.

Vehemence; fury; impetuosity; as the fierceness of a tempest.

fierceness ‎(usually uncountable, plural fiercenesses)

- 1749, John Cleland, Fanny Hill: Memoirs of a Woman of Pleasure, Part 5
  I stroked it gently, on which the mutinous rogue seemed to swell, and gather a new degree of fierceness and insolence; so that finding it grew not to be trifled with any longer, I prepar'd for rubbers in good earnest.

state of being fierce